Traffic accidents often occur due to driver impairment caused by, for example, drowsiness, illness, distraction, intoxication, etc. In order to prevent accidents caused by driver impairment, it may be vital to provide the driver with a warning message to re-establish the attention of the driver to the surrounding traffic situation, or in a critical situation to advice the driver to take a break or switch to another driver of the vehicle.
Several systems are known which attempt to predict the behaviour of the driver and provide the driver with a warning message in the event that he/she is not aware of the current driving situation or the environment of the vehicle. However, it may be vital to provide a warning message which the driver is capable to assimilate and react to. In other words, it may be vital to provide different warning messages for different causes of driver impairment. For example, a drowsy driver should be given a warning message intended for drowsiness and not a message intended for e.g. an intoxicated or distracted driver. A warning message intended for e.g. a distracted driver when the driver in fact is drowsy, may result in that the driver does not assimilate and react to the message in a correct and desired way.
U.S. Pat. No. 6,974,414 describes a system for monitoring the physiological behaviour of a driver. The system measures, for example, the driver's eye movement, eye-gaze direction, eye-closure amount, blinking movements, head movements, etc. A warning message is provided to the driver of the vehicle when the system detects one of a plurality of physiological behaviour that may cause an accident.
However, this system, as well as other known systems, may not discriminate well between the actual causes for the driver impairment, i.e. to specifically determine the casual factors behind a measured impairment. It is thus desirable to provide a system for improving performance estimation of the vehicle driver.